Haemolysis in Ball Valves With Overlapping and Non-Overlapping Closing Mechanisms:An Experimental Study

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Abstract
Overlapping and non-overlapping closing mechanisms of the ball valve type were evaluated in regard to rates of haemolysis. the test chamber used in this experimental study permitted an almost physiological valve function in a minimal volume of human whole blood. An overlapping closing mechanism was represented by the Starr-Edwards aortic silastic ball valve and a non-overlapping one by the Smeloff-Cutter aortic silastic ball valve. Red cell destruction was significantly lower with a non-overlapping ball than with an overlapping one on valve closure. the magnitude of red cells destroyed in 80 ml of blood/hour was, on average, 0.29 % and 0.73 % respectively. the Bjork-Shiley tilting disc valve was tested as a control and accounted for a red cell destruction of 0.20%. Assuming a linear progression of haemolysis with time, a blood volume of 4 800 ml, and a normal erythrocyte survival time of 120 days, the red cell destruction attributable to the prosthetic closing mechanisms could be extrapolated to in uiuo conditions. the production rate of red cells by the bone marrow would have to increase by 14% in a patient with a single Smeloff-Cutter valve replacement in order to prevent the development of anaemia. in a patient with single Starr-Edwards valve replacement, a corresponding value of 34% was calculated. These values would increase two or three fold after double or triple valve replacement. An overlapping closing mechanism has again been shown to cause a significantly larger degree of haemolysis than non-overlapping mechanism, presumably due to the mechanical crushing of red cells.